I've got 5 gallons of a sour blonde ale that I made about a year ago and it's pretty good at the moment but I'm looking to add some fruit to it (at least part of the batch).

I wanted to use grapes, sort of in the vain of some of my favorite beers (Cantillon St. Lamvinus, Russian River Depuration, Russian River Temptation, etc.). Ideally, I would like to use Chardonnay grapes, but this is where my questions begins.

Where can I buy (reasonably priced) grapes? I know some homebrew stores have wine kits available, but I don't really want to spend $100 for a wine kit when all I want is the fruit for a few gallons of beer (plus, these all seem to just be juice).

Failing the ability to get some wine grapes, would it be worthwhile to use regular table grapes like those available at the grocery store/farmer's market/etc.?

Yeah you should have a few wineries around you. And harvest time is coming up. Typically the month of September is harvest time. Which sounds like it should be good timing.
My home winemaker friend usually buys the juice from them but I'm sure you could buy whole grapes too.
And table grapes are very different than wine grapes. I don't have any experience with making wine with them but you could ask some one in the Wine section of the forum.
I'm going to do a similar thing this winter with a triple I want to sour. I was thinking zin grapes.

I can understand where your coming from, I planted some cab and merlot grapes for doing this very thing

You might be able to find some at whole foods from time to time I see champagne grapes etc there, they are kinda pricey though

As to using table grapes, most wont do anything in a sour, their flavor is so light and for the most part it would be like adding some sugar, now with that said I have had a muscat sour, and that was quite good, muscats do have quite a bit stronger flavor than most though

You might be able to find some at whole foods from time to time I see champagne grapes etc there, they are kinda pricey though

As to using table grapes, most wont do anything in a sour, their flavor is so light and for the most part it would be like adding some sugar, now with that said I have had a muscat sour, and that was quite good, muscats do have quite a bit stronger flavor than most though

That was my thought. I've recently seen champagne grapes at the grocery store. They looked expensive, but I didn't check the prices.

As other people said, check out winemaking juice/must/whatever-they-call-it or check with nearby wineries. Some of the wineries I've visited have rows of grapes they grow purely to fertilize the field, so you might be able to convince them to sell you a small amount of those grapes for very little. It's certainly worth a few phone calls. You might also find local winemakers who grow wine grapes in their backyard. I'm sure you could convince somebody to sell you some. Try finding them on craigslist or another local forum.

The grapes labeled "Champagne" grapes... those aren't actually the grapes used to make Champagne. The grapes used in making actual Champagne vary, but tend to be the typical vinifera grapes used in making other French wines (Chardonnay, Pinot Noir, etc.) "Champagne" is a reference to a place, not a specific variety of grape.

The little "champagne" grapes you buy in the store are the ones that are dried into zante currants.

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